LUNAR DATA SUPPORT IDEA THAT COLLISION SPLIT EARTH, MOON

Analysis of data from NASA's Lunar Prospector spacecraft has
Analysis of data from NASA's Lunar Prospector spacecraft has
confirmed that the Moon has a small core, supporting the theory
that the bulk of the Moon was ripped away from the early Earth
when an object the size of Mars collided with the Earth.

Scientists presented this result and other findings today in
a series of papers at the 30th Lunar and Planetary Science
Conference in Houston, TX. Their data show that the lunar core
contains less than four percent of the Moon's total mass, with the
probable value being two percent or slightly less. This is very
small when compared with the Earth, whose iron core contains
approximately 30 percent of the planet's mass.

"This is a critical finding in helping scientists determine
how the Earth and Moon formed," said Dr. Alan Binder of the Lunar
Research Institute, Tucson, AZ, principal investigator for Lunar Prospector.

Similarities in the mineral composition of the Earth and the
Moon indicate that they share a common origin. However, if they
had simply formed from the same cloud of rocks and dust, the Moon
would have a core similar in proportion to the Earth's. A third
theory suggests that the moon was captured fully intact by the Earth's gravity.

Based on information first gathered during the Apollo era,
scientists suggested that the Moon was formed when a Mars-sized
body hit the Earth during its earliest history. "This impact
occurred after the Earth's iron core had formed, ejecting rocky,
iron-poor material from the outer shell into orbit," Binder
explained. "It was this material that collected to form the Moon.

"Further analysis of Lunar Prospector data to refine the
exact size of the lunar core and the amounts of elements like
gold, platinum and iridium in lunar rocks -- all of which are
concentrated with metallic iron -- is required," Binder added.
"This will do much to pin down for good if the 'giant impact'
model of the formation of the Moon is correct, or if the Moon
formed in a different manner."

The current data come from gravity measurements conducted by
Dr. Alex Konopliv of NASA's Jet Propulsion Laboratory, Pasadena,
CA. His results indicate that the Moon's core radius is between
140 and 280 miles (220 and 450 kilometers). This result is
consistent with independent magnetic data, evaluated by Dr. Lon
Hood of the University of Arizona, Tucson, which suggest that the
core radius is between 180 and 260 miles (300 and 425 km).

In other results from Lunar Prospector, Dr. Robert Lin of the
University of California at Berkeley, Dr. Mario Acu–a of NASA's
Goddard Space Flight Center, Greenbelt, MD, and Hood also found
that a broad section of the southern far-side of the Moon has
large localized magnetic fields in its crust. These fields occur
opposite the large Crisium, Serenitatis and Imbrium basins --
three of the "seas" that cover much of the Moon's near side. This
result supports earlier evidence linking strong magnetized
concentrations on one side of the Moon with young, large impact
basins on the other side.

Results of efforts to map the composition of the lunar crust
have surpassed the expectations of the spectrometer team, led by
Dr. William Feldman of the Department of Energy's Los Alamos
National Laboratory in New Mexico. Data obtained are so good that
the distribution of thorium has been mapped with a resolution of
36 miles (60 kilometers). At this amount of detail, scientists
can detect individual deposits rich in thorium and related
elements. Their current observations suggest that thorium was
excavated by impacts of asteroids and comets, and then distributed
around craters, rather than being deposited by volcanic activity.

Lunar Prospector conducted its primary mapping mission at an
altitude of 63 miles (100 kilometers) for almost one year after
its arrival in lunar orbit on Jan. 11, 1998. In December and
January, the spacecraft's altitude was lowered to approximately 15
miles by 23 miles (24 kilometers by 37 kilometers). Analyses of
data from the lower-altitude observations are expected to further
improve scientific understanding of the origin, evolution and
physical resources of the Moon.

The $63 million mission is managed by NASA's Ames Research
Center, Moffett Field, CA, and was developed under NASA's
Discovery Program of lower-cost, highly focused small scientific spacecraft.